Fixation of 5-Unit Implant-Supported Fixed Partial Dentures and Resulting Bone Loading: A Finite Element Assessment Based on In Vivo Strain Measurements

Purpose: It is believed that implant-supported fixed partial dentures (FPDs) should display passive fit. The objective of this in vivo-based finite element analysis (FEA) was to quantify the magnitude of bone loading occurring on account of the fixation of cemented or screw-retained 5-unit superstructures. Materials and Methods: Based on a patient situation with 3 implants, 4 different groups of restorations with 10 samples each were fabricated. Strain gauges on the pontics of the restorations were used for in vivo measurements. Using the values obtained, bone loading in 3-dimensional FE models was simulated as von Mises equivalent stress. Results: The in vivo measured mean strain values ranged from 32 µm/m to 458 µm/m at the different sites. FEA revealed stresses between 5 and 30 MPa in the cortical area, while in trabecular bone values ranging from 2 MPa to 5 MPa were observed. Stress of a similar magnitude was found for axial implant loading with 200 N. Discussion: Assuming that the axial loading of a single implant with 200 N is within the realm of the bone's adaptation ability, it would appear that the amount of stress resulting from the fixation of superstructures alone does not constitute a risk. Conclusions: The level of precision of fit which can be obtained in superstructure fabrication would appear to suffice to produce restorations that do not cause bone damage. Schlagwörter: bone loading, cement fixation, finite element analysis, in vivo strain measurements, passive fit, screw retention